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Vulnerability Intelligence Report
NGINX ngx_http_rewrite_module vulnerability

CVE-2026-9256

x_F5

NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_rewrite_module module. This vulnerability exists when a rewrite directive uses a regex pattern with distinct, overlapping Perl-Compatible Regular Expression (PCRE) captures (for example, ^/((.*))$) and a replacement string that references multiple such captures (for example, $1$2) in a redirect or arguments context. An unauthenticated attacker along with conditions beyond their control can exploit this vulnerability by sending crafted HTTP requests. This may cause a heap buffer overflow in the NGINX worker process leading to a restart. Additionally, attackers can execute code on systems with Address Space Layout Randomization (ASLR) disabled or when the attacker can bypass ASLR. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

No Active Exploit Signals
CVSS Base Score
8.1
HIGH
Exploitability:2.3
Impact Score:5.9
EPSS Probability:9.96%
Executive Threat Verdict
Evaluating...
Evaluating Threat Landscape...
Assessing known weaponization, exploitation telemetry, and federal advisories.
Attack Surface
Authentication
Weaponization
SSVC Action

Weaknesses (CWE)

CWE-122 ↗CWE-122 Heap-based Buffer Overflow

Affected Products & Versions

Vendor Product Affected Versions
F5 NGINX Plus 37.0 < 37.0.1.1 (affected), R36 < R36 P5 (affected), R32 < R32 P7 (affected)
F5 NGINX Open Source 1.31.0 < 1.31.1 (affected), 1.30.0 < 1.30.2 (affected), 0.1.17 <= 0.9.7 (affected)

References & Technical Advisories

No reference links found.

Threat Intelligence Signals

EPSS Score
9.963%

Identity & Timeline

StatusPUBLISHED
Assigning AuthorityF5, Inc. · Vendor · USA
Reserved2026-05-21T20:58:58
Published2026-05-22T14:11:41
Patch Date2026-05-22
Last Updated2026-08-25T12:05:55

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